Parallel circuit comprising a plurality of IGBTs

ABSTRACT

In a parallel circuit ( 10 ) comprising a plurality of high-power IGBTs (T 1 , . . . ,T 3 ) which are each driven by a dedicated gate drive circuit (GD 1, . . . ,GD 3 ), each of the gate drive circuits (GD 1, . . . ,GD 3 ) having, at its output, a p-channel MOSFET (M 1,  M 3,  M 5 ) and an n-channel MOSFET (M 2,  M 4,  M 6 ) in a push-pull arrangement and the outputs of the gate drive circuits (GD 1,  . . . ,GD 3 ) being connected to the gates of the IGBTs (T 1, . . . ,T 3 ) in each case via a gate resistor (R 1, . . . ,R 3 ), a parallel circuit comprising more than two gate drive circuits is made possible by virtue of the fact that the outputs of the gate drive circuits (GD 1, . . . ,GD 3 ) are interconnected via a connecting line ( 11 ), and that the MOSFETs (M 1, . . . ,M 6 ) of the gate drive circuits (GD 1, . . . ,GD 3 ) are in each case connected to a positive or negative supply terminal (P 1,  . . . ,P 3  or N 1 , . . . ,N 3 ) via a constant-current source (CS 1, . . . ,CS 6 ).

FIELD OF THE INVENTION

The present invention concerns the field of power electronics. Itrelates to a parallel circuit comprising a plurality of IGBTs.

BACKGROUND OF THE INVENTION

For a relatively long time power electronic semiconductor modules havebeen commercially available in which up to six high-power IGBTs withcorresponding reverse-connected parallel diodes are arranged andinterconnected in such a way that they can either form the individualarms of a three-phase power converter bridge or can be combined by beingconnected in parallel to form a single phase arm with three-foldcurrent-carrying capacity. Modules of this type are offered by theapplicant under the general type designation LoPak5 and have, by way ofexample, a collector-emitter voltage V_(CE) of 1200 V and a collectorcurrent I_(c) of 300 A (see the data sheet 5SYA1528 from ABBSemiconductors AG relating to the module type 5SNS030OU120100 of Jul. 1,2000).

The parallel circuit comprising such high-power IGBTs on the power side(i.e. by connecting the collector-emitter paths of the individual IGBTsin parallel) throws up various problems:

If the IGBTs with their associated gate drive circuits (“gate drives”)are only connected in parallel on the power side without furthermeasures, considerable unequal distribution of the currents between theindividual IGBTs can occur dynamically due to different delays in thegate drive circuits during the switching of the IGBTs. Since theindividual gates of the IGBTs are not connected to one another, thepositive transistor behavior of the IGBTs does not help either.

If the gates of the IGBTs are likewise connected in parallel, the IGBTs,owing to their fundamental transistor behavior, naturally have thetendency to statically divide the currents identically among themselves:identical transistors have identical I_(CE)/V_(CE) characteristics and -since they have the same V_(CE) and the same gate voltage - they mustalso draw the same collector-emitter current I_(CE). Dynamically,however, the currents can differ considerably. The absolute values ofthe gate resistances as well as the ratio of individual and commonresistances in the module influence the balance between the currents.

The output stage of a gate drive circuit used for such IGBTs is usuallya push-pull stage constructed with two MOSFETs (p-channel and n-channelMOSFETs). If two gate drive circuits are connected in parallel, it mustbe ensured that one gate drive circuit does not break down to the otherand that one gate drive circuit does not “charge” the other. Thesimplest solution is to use individual gate resistors for decoupling thegate drive circuits. However, such a solution can only be realized fortwo gate drive circuits connected in parallel.

SUMMARY OF THE INVENTION

It is an object of the invention, therefore, to specify a parallelcircuit comprising high-power IGBTs in which more than two gate drivecircuits are connected in parallel.

The essence of the invention is that the MOSFETs in the output stages ofthe gate drive circuits are in each case connected to a positive ornegative supply terminal via a constant-current source and the outputsof the gate drive circuits are interconnected via a connecting line. Inthis case, the constant-current sources are designed as “weak”constant-current sources and are constructed in a manner known per sefrom a transistor or MOSFET and diodes and/or resistors.

In order that the power supplies of the gate drive circuits are at leastuniformly loaded, it is advantageous if the positive and negative supplyterminals of the gate drive circuits are respectively interconnected byconnecting lines.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below using an exemplaryembodiment in connection with the drawing. The single figure shows thecircuit diagram of a preferred exemplary embodiment of a parallelcircuit according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The figure illustrates a parallel circuit comprising three IGBTs T1, . .. ,T3 in accordance with a preferred exemplary embodiment of theinvention. The IGBTs (Insulated Gate Bipolar Transistors) T1, . . . ,T3with their reverse-connected parallel diodes D1, . . . ,D3 may, forexample, be part of a power semiconductor module, as was mentioned inthe introduction, and as is used to form controlled power converterbridges. The IGBTs are connected in parallel on the power side and thusform, for example, an arm of a power converter bridge with three-foldcurrent-carrying capacity. Each of the IGBTs T1, . . . ,T3 is driven byan associated gate drive circuit (“gate drive”) GD1, . . . ,GD3 via agate resistor R1, . . . ,R3, of which drive circuit only the outputstage equipped with MOSFETs M1, . . . ,M6 is illustrated, for the sakeof simplicity.

In each of the gate drive circuits GD1, . . . ,GD3, a p-channel MOSFET(M1, M3, M5) and an n-channel MOSFET (M2, M4, M6) in a push-pullarrangement are provided in the output stage. Each of the MOSFETs M1 , .. . ,M6 is connected to a positive or negative supply terminal P1, . . .,P3 or N1, . . . ,N3 via an associated constant-current source CS1, . .. , CS6. The constant-current sources CS1, . . . , CS6 are constructedas “weak” constant-current sources from a transistor or MOSFET anddiodes and/or resistors.

The outputs of the gate drive circuits GD1, . . . ,GD3, i.e. thejunction points between the MOSFET pairs in the output stage, areinterconnected via a common first connecting line 11, and are thusconnected in parallel. The positive supply terminals P1, . . . ,P3 areinterconnected by a second connecting line 12 and the negative supplyterminals N1, . . . ,N3 are interconnected by a third connecting line13.

Although the problem of unequal distribution of the loading between thegate drive circuits GD1, . . . , GD3 remains, i.e. the gate drivecircuits to be driven first is always subjected to the greatest loading,the loading is limited to a predetermined value by the circuitconstruction according to the invention. At the same time, the powersupplies of the gate drive circuits GD1, . . . , GD3 are uniformlyloaded by the connection of the supply terminals P1, . . . , P3 and N1,. . .,N3.

LIST OF REFERENCE SYMBOLS

10 Parallel circuit

11 Connecting line (gate drive circuit)

12, 13 Connecting line (supply terminals)

CS1, . . . , CS6Constant-current source

D1, . . . , D3 Diode

GD1, . . . , GD3 Gate drive circuit (gate drive)

M1, . . . , M6 MOSFET transistor

N1, . . . , N3 Negative supply terminal

P1, . . . , P3 Positive supply terminal

R1, . . . , R3 Gate resistor

T1, . . . , T3 IGBT

What is claimed is:
 1. A parallel circuit comprising a plurality ofhigh-power IGBTs which are each driven by a dedicated gate drivecircuit, each of the gate drive circuits having, at its output, ap-channel MOSFET and an n-channel MOSFET in a push-pull arrangement andthe outputs of the gate drive circuits being connected to the gates ofthe IGBTs in each case via a gate resistor, wherein the outputs of thegate drive circuits are interconnected via a connecting line, and inthat the MOSFETs of the gate drive circuits are in each case connectedto a positive or negative supply terminal via a constant-current source.
 2. The parallel circuit as claimed in claim 1, wherein theconstant-current sources are constructed from a) a transistor or MOSFET,and b) diodes and/or resistors.
 3. The parallel circuit as claimed inclaim 1, wherein the positive and negative supply terminals of the gatedrive circuits are respectively interconnected by connecting lines.